Integrated microsystems have a number of important applications, especially in the field of biological material analysis. Such systems typically direct a light source at a sample and detect the light reflected from, transmitted through, or fluorescing from the sample.
One problem impeding wide adaptation of such integrated microsystems is the cost and complexity of such systems. In order to minimize cross contamination between biological samples, microchannels carrying the biological samples are typically designed to be disposable. Thus each microsystem needs to be inexpensive and simple to fabricate.
Microfluidic devices are generally made by subtractive processes, such as etching features into a glass or silicon substrate (“Micromachining a Miniaturized Capillary Electrophoresis-Based Chemical Analysis System on a Chip” Harrison, D. J.; Fluri, K.; Seiler, K.; Fan, Z.; Effenhauser, C. S.; Manz, A.; Science 1993 261 895-897), or by a molding procedure, typically using a polymeric material (“Integrated Capillary Electrophoresis on Flexible Silicone Microdevices: Analysis of DNA Restriction Fragments and Detection of Single DNA Molecules on Microchips” Effenhauser, C. S.; Bruin, G. J. M.; Paulus, A.; Ehrat, M.; Anal. Chem.; 1997; 69(17); 3451-3457). As will be explained, these processes impart limitations on the fabrication of totally integrated devices.
Both microfluidic channels and electronic elements can be fabricated using conventional processing on silicon substrates (“An Integrated Nanoliter DNA Analysis Device” M. A. Burns, B. N. Johnson, S. N. Brahmasandra, K. Handique, J. R. Webster, M. Krishnan, T. S. Sammarco, P. M. Man, D. Jones, D. Heldsinger, C. H. Mastrangelo, and D. T. Burke; Science 1998 Oct. 16; 282: 484-487). Typically, the same substrate material is used to form the passive fluidic channels and to serve as the growth substrate upon which the active electronic devices are grown. However, such techniques result in a low density of active devices being processed on each growth substrate because the passive channels typically cover a large area relative to the electronic devices. The high cost of silicon processing associated with active device formation and the low density of active devices on the growth substrate makes this process expensive. In addition, it may be difficult to add components from other solid-state materials such as III-V semiconductors.
Molding procedures are sometimes used to fabricate passive microfluidic channel structures. While molding can be done with relatively high precision, it is difficult to integrate active electronic devices with good registration between the channels and electronic devices using conventional molding processes (“An Integrated Fluorescence Detection System in Poly(dimethylsiloxane) for Microfluidic Applications” M. L. Chabinyc, D. T. Chiu, J. C. McDonald, A. D. Stroock, J. F. Christian, A. M. Karger, G. M. Whitesides, and “Fluidics Cube for Biosensor Miniaturization”; J. M. Dodson, M. J. Feldstein, D. M. Leatzow, L K. Flack, J. P. Golden, and F. S. Ligler Anal. Chem., 73 (15), 3776-3780, 2001).
Another difficulty with current fabrication techniques is that combining dissimilar elements by direct growth and micromachining on the same substrate to form a single integrated unit has proven to be technically difficult. For example, the microchannels, the semiconductor light emitters and detectors are formed from materials that are incompatible such that fabrication together in a single process results in poor quality devices. This incompatibility stems partly from the fact that thermal processing stability and thermal management techniques used in the fabrication of most high efficiency optoelectronic light sources are incompatible with the formation of plastic or glass structures that are typically used to form a microchannel.
Thus an improved method of fabricating a microsystem that integrates a micro-fluidic channel aligned with other electronic or opto-electronic component onto a single platform at a reduced cost and complexity is desired.